The present invention relates to retroreflective sheeting employing microprism formations to retroreflect the light rays impinging thereon, and, more particularly, to a method for producing such retroreflective sheet material which provides a bright coloration in daylight and ambient light and which is also highly retroreflective when exposed to light beams at night.
Retroreflective sheet material is widely employed for a variety of safety and decorative purposes, and is particularly useful when the need for night time visibility is significant under conditions of low ambient light. In retroreflective materials, the light rays impinging upon the front surface are reflected back towards the source of the illumination in a substantially parallel path. In situations where headlights or search lights on boats and aircraft are the only source of illumination, this ability to retroreflect the bulk of the rays falling thereon is especially significant for warning signs, delineators and the like.
Minnesota Mining and Manufacturing Corporation has manufactured retroreflective sheeting utilizing minute glass beads embedded in a matrix of synthetic resin to provide such retroreflection, and these materials have been sold under the trademark SCOTCHLITE. Illustrative of such materials is Bergeson et al U.S. Pat. No. 4,637,950 granted Jan. 20, 1987.
Applicant's assignee, Reflexite Corporation, has been marketing under the trademark REFLEXITE, reflective sheeting employing microprisms formations to produce such retroreflection Illustrative of such materials is Rowland U.S. Pat. No. 3,689,346 granted Sep. 5, 1972.
In Martin U.S. Pat. No. 4,801,193 granted Jan. 31, 1989, there is described in detail a process for producing grid patterns of metallized and unmetallized prisms, and the use of adhesive spacing to provide an air backing about prisms.
Among the applications for such retroreflective materials are reflective tapes and patches for clothing of firemen, reflective vests and belts, bands for posts and barrels, traffic cone collars, highway signs, warning reflectors, and the like.
It is desirable for some applications that the retroreflective sheeting exhibit a bright coloration in daylight and ambient light, such as the red and yellow/green used for warning and emergency. In Rowland U.S. Pat. No. 3,830,682 granted Aug. 20, 1974, a metameric dye is included so that the sheet material fluoresces in one color in daylight and retroreflects in a second coloration when exposed to headlights and other directional light sources at night.
The use of a metallized aluminum coating on the prism surfaces tends to produce a grey coloration to the observer in ambient light or daylight conditions. In some applications, this grey appearance is considered aesthetically undesirable, and coloration would be desirable.
It is an object of the present invention to provide a novel retroreflective sheeting using microprism formations which exhibits a bright coloration in daylight and high retroreflectivity at night when exposed to directional light sources.
It is also an object of the present invention to provide such a colored retroreflective sheet material which may be readily fabricated and which is durable and resistant to the elements.
Another object of the present invention is to provide novel methods for fabricating such retroreflective sheet material which are relatively simple and relatively economical, and which produce long-lived materials.